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11
Macronutrients and
Healthful Diets
SUMMARY
Acceptable Macronutrient Distribution Ranges (AMDRs) for indi-
viduals have been set for carbohydrate, fat, n-6 and n-3 poly-
unsaturated fatty acids, and protein based on evidence from
interventional trials, with support of epidemiological evidence that
suggests a role in the prevention or increased risk of chronic dis-
eases, and based on ensuring sufficient intakes of essential nutrients.
The AMDR for fat and carbohydrate is estimated to be 20 to 35
and 45 to 65 percent of energy for adults, respectively. These
AMDRs are estimated based on evidence indicating a risk for coro-
nary heart disease (CHD) at low intakes of fat and high intakes of
carbohydrate and on evidence for increased risk for obesity and
its complications (including CHD) at high intakes of fat. Because
the evidence is less clear on whether low or high fat intakes during
childhood can lead to increased risk of chronic diseases later in
life, the estimated AMDRs for fat for children are primarily based
on a transition from the high fat intakes that occur during infancy
to the lower adult AMDR. The AMDR for fat is 30 to 40 percent of
energy for children 1 to 3 years of age and 25 to 35 percent
of energy for children 4 to 18 years of age. The AMDR for carbo-
hydrate for children is the same as that for adults—45 to 65 percent
of energy. The AMDR for protein is 10 to 35 percent of energy for
adults and 5 to 20 percent and 10 to 30 percent for children 1
to 3 years of age and 4 to 18 years of age, respectively.
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Based on usual median intakes of energy, it is estimated that a
lower boundary level of 5 percent of energy will meet the Adequate
Intake (AI) for linoleic acid (Chapter 8). An upper boundary for
linoleic acid is set at 10 percent of energy for three reasons:
(1) individual dietary intakes in the North American population
rarely exceed 10 percent of energy, (2) epidemiological evidence
for the safety of intakes greater than 10 percent of energy are
generally lacking, and (3) high intakes of linoleic acid create a
pro-oxidant state that may predispose to several chronic diseases,
such as CHD and cancer. Therefore, an AMDR of 5 to 10 percent
of energy is estimated for n-6 polyunsaturated fatty acids (linoleic
acid).
An AMDR for α-linolenic acid is estimated to be 0.6 to 1.2 percent
of energy. The lower boundary of the range meets the AI for
α-linolenic acid (Chapter 8). The upper boundary corresponds to
the highest α-linolenic acid intakes from foods consumed by indi-
viduals in the United States and Canada. A growing body of litera-
ture suggests that higher intakes of α-linolenic acid, eicosapentaenoic
acid (EPA), and docosahexaenoic acid (DHA) may afford some
degree of protection against CHD. Because the physiological
potency of EPA and DHA is much greater than that for α-linolenic
acid, it is not possible to estimate one AMDR for all n-3 fatty acids.
Approximately 10 percent of the AMDR can be consumed as EPA
and/or DHA.
No more than 25 percent of energy should be consumed as added
sugars. This maximal intake level is based on ensuring sufficient
intakes of certain essential micronutrients that are not present in
foods and beverages that contain added sugars. A daily intake of
added sugars that individuals should aim for to achieve a healthy
diet was not set.
A Tolerable Upper Intake Level (UL) was not set for saturated
fatty acids, trans fatty acids, or cholesterol (see Chapters 8 and 9).
This chapter provides some guidance in ways of minimizing the
intakes of these three nutrients while consuming a nutritionally
adequate diet.
INTRODUCTION
Unlike micronutrients, macronutrients (fat, carbohydrate, and pro-
tein) are sources of body fuel that can be used somewhat interchangeably.
Thus, for a certain level of energy intake, increasing the proportion of one
macronutrient necessitates decreasing the proportion of one or both of
the other macronutrients. The majority of energy is consumed as carbo-

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M ACRONUTRIENTS AND HEALTHFUL DIETS
hydrate (approximately 35 to 70 percent, primarily as starch and sugars),
and fat (approximately 20 to 45 percent), while the contribution of protein
to energy intake is smaller and less varied (10 to 23 percent) (Appendix
Tables E-3, E-6, and E-17). Therefore, a high fat diet (high percent of
energy from fat) is usually low in carbohydrate and vice versa. In addition
to these macronutrients, alcohol can provide on average up to 3 percent
of energy of the adult diet (Appendix Table E-18).
A small amount of carbohydrate and as n-6 (linoleic acid) and n-3
(α-linolenic acid) polyunsaturated fatty acids and a number of amino acids
that are essential for metabolic and physiological processes, are needed by
the brain. The amounts needed, however, each constitute only a small
percentage of total energy requirements. Food sources vary in their con-
tent of particular macro- and micronutrients. While some nutrients are
present in both animal- and plant-derived foods, others are only present
or are more abundant in either animal or plant foods. For example,
animal-derived foods contain significant amounts of protein, saturated fatty
acids, long-chain n-3 polyunsaturated fatty acids, and the micronutrients
iron, zinc, and vitamin B12, while plant-derived foods provide greater
amounts of carbohydrate, Dietary Fiber, linoleic and α-linolenic acids, and
micronutrients such as vitamin C and the B vitamins. It may be difficult to
achieve sufficient intakes of certain micronutrients when consuming foods
that contain very low amounts of a particular macronutrient. Alternatively,
if intake of certain macronutrients from nutrient-poor sources is too high,
it may also be difficult to consume sufficient micronutrients and still
remain in energy balance. Therefore, a diet containing a variety of foods is
considered the best approach to ensure sufficient intakes of all nutrients.
This concept is not new and has been part of nutrition education pro-
grams since the early 1900s. For example, the first U.S. food guide was
developed by the U.S. Department of Agriculture in 1916 and suggested
consumption of a combination of five different food groups (Guthrie and
Derby, 1998). This food guide has evolved to become known as the Food
Guide Pyramid (USDA, 1996). Similarly, Canada has developed Canada’s
Food Guide to Healthy Eating (Health Canada, 1997).
A growing body of evidence indicates that an imbalance in macro-
nutrients (e.g., low or high percent of energy), particularly with certain
fatty acids and relative amounts of fat and carbohydrate, can increase risk
of several chronic diseases. Much of this evidence is based on epidemio-
logical studies of clinical endpoints such as coronary heart disease (CHD),
diabetes, cancer, and obesity. However, these studies demonstrate associa-
tions; they do not necessarily infer causality, such as would be derived
from controlled clinical trials. Robust clinical trials with specified clinical
endpoints are generally lacking for macronutrients. Of importance, fac-
tors other than diet contribute to chronic disease, and multifactorial cau-

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sality of chronic disease can confound the long-term adverse effects of a
given macronutrient distribution. It is not possible to determine a defined
level of intake at which chronic disease may be prevented or may develop.
For example, high fat diets may predispose to obesity, but at what percent
of energy intake does this occur? The answer depends on whether energy
intake exceeds energy expenditure or is balanced with physical activity.
This chapter reviews the scientific evidence on the role of macro-
nutrients in the development of chronic disease. In addition, the nutrient
limitations that can occur with the consumption of too little or too much
of a particular macronutrient are discussed. In consideration of the inter-
relatedness of macronutrients, their role in chronic disease, and their
association with other essential nutrients in the diet, Acceptable Macro-
nutrient Distribution Ranges (AMDRs) are estimated and represented as
percent of energy intake. These ranges represent (1) intakes that are asso-
ciated with reduced risk of chronic disease, (2) intakes at which essential
dietary nutrients can be consumed at sufficient levels, and (3) intakes
based on adequate energy intake and physical activity to maintain energy
balance. When intakes of macronutrients fall above or below the AMDR,
the risk for development of chronic disease (e.g., diabetes, CHD, cancer)
appears to increase.
DIETARY FAT AND CARBOHYDRATE
There are a number of adverse health effects that may result from
consuming a diet that is too low or high in fat or carbohydrate (starch and
sugars). Furthermore, chronic consumption of a low fat, high carbohydrate
or high fat, low carbohydrate diet may result in the inadequate intake of
certain essential nutrients.
Low Fat, High Carbohydrate Diets of Adults
The chronic diseases of greatest concern with respect to relative intakes
of macronutrients are CHD, diabetes, and cancer. In this section, the rela-
tionship between total fat and total carbohydrate intakes are considered.
Comparisons are made in terms of percentage of total energy intake. For
example, a low fat diet signifies a lower percentage of fat relative to total
energy. It does not imply that total energy intake is reduced because of
consumption of a low amount of fat. The distinction between hypocaloric
diets and isocaloric diets is important, particularly with respect to impact on
body weight. Low and high fat diets can still be isocaloric. The failure to
identify this distinction has led to considerable confusion in terms of the
role of dietary fat in chronic disease.

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In the past few decades, the prevalence of overweight and obesity has
increased at an alarming rate in many populations, particularly in the
United States. Overweight and obesity contribute significantly to various
chronic diseases. Consequently, there are two issues to consider for the
distribution of fat and carbohydrate intakes in high-risk populations: the
distributions that predispose to the development of overweight and obesity,
and the distributions that worsen the metabolic consequences in popula-
tions that are already overweight or obese. These issues will be considered
in the following sections.
Maintenance of Body Weight
A first issue is whether a certain macronutrient distribution interferes
with sufficient intake of total energy, that is, sufficient energy to maintain
a healthy weight. Sonko and coworkers (1994) concluded that an intake of
15 percent fat was too low to maintain body weight in women, whereas an
intake of 18 percent fat was shown to be adequate even with a high level of
physical activity (Jéquier, 1999). Moreover, some populations, such as those
in Asia, have habitual very low fat intakes (about 10 percent of total energy)
and apparently maintain adequate health (Weisburger, 1988). Whether
these low fat intakes and consequent low energy consumptions have con-
tributed to a historically small stature in these populations is uncertain.
An issue of more importance for well-nourished but sedentary popula-
tions, such as that of the United States, is whether the distribution between
intakes of total fat and total carbohydrate influences the risk for weight
gain (i.e., for development of overweight or obesity). It has been shown
that when men and women were fed isocaloric diets containing 20, 40, or
60 percent fat, there was no difference in total daily energy expenditure
(Hill et al., 1991). Similar observations were reported for individuals who
consumed diets containing 10, 40, or 70 percent fat, where no change in
body weight was observed (Leibel et al., 1992), and for men fed diets
containing 9 to 79 percent fat (Shetty et al., 1994). Horvath and colleagues
(2000) reported no change in body weight after runners consumed a diet
containing 16 percent fat for 4 weeks. These studies contain two important
findings: fat and carbohydrate provide similar amounts of metabolic energy
predicted from their true energy content, and isocaloric diets provide
similar metabolic energy expenditure, regardless of their fat–carbohydrate
distribution. In other words, at isocaloric intakes, low fat diets do not
produce weight loss.
A number of short- and long-term intervention studies have been con-
ducted on normal-weight or moderately obese individuals to ascertain the
effects of altering the fat and energy density content of the diet on body
weight (Table 11-1). In general, significant reductions in the percent of

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energy consumed as fat (greater than 4 percent) resulted in small losses in
body weight. The only study that provided isocaloric diets showed no dif-
ferences in weight gain or loss, despite a wide range in the percent of
energy from fat (Leibel et al., 1992). Four meta-analyses of long-term
intervention studies associating a low fat diet with body weight concluded
that lower fat diets lead to modest weight loss or prevention of weight gain
(Astrup et al., 2000; Bray and Popkin, 1998; Hill et al., 2000; Yu-Poth et al.,
1999). These studies thus suggest that low fat diets (low percentage of fat)
tend to be slightly hypocaloric compared to higher fat diets when com-
pared in outpatient intervention trials.
The finding that higher fat diets are moderately hypercaloric when
compared with reduced fat intakes under ad libitum conditions provides a
rationale for setting an upper boundary for percentage of fat intake in a
population that already has a high prevalence of overweight and obesity.
However, a second issue must also be addressed: whether the distribution
of fat and carbohydrate modifies the metabolic consequences of over-
weight and obesity. Two of the more important consequences of obesity
are dyslipidemic changes in serum lipoproteins (which predispose to CHD)
and changes in glucose and insulin metabolism that accentuate an under-
lying insulin resistance (which may predispose to both CHD and diabetes).
These consequences are discussed in the following sections.
Risk of CHD
Low fat, high carbohydrate diets, compared to higher fat intakes, can
induce a lipoprotein pattern called the atherogenic lipoprotein pheno-
type (Krauss, 2001) or atherogenic dyslipidemia (National Cholesterol
Education Program, 2001). In populations where people are routinely
physically active and lean, the atherogenic lipoprotein phenotype is mini-
mally expressed. In sedentary populations that tend to be overweight or
obese, very low fat, high carbohydrate diets clearly promote the develop-
ment of this phenotype. Whether this phenotype promotes development
of coronary atherosclerosis when it is specifically induced by low fat diets is
uncertain, but it is a pattern that is associated with increased risk for CHD
when expressed in the general American population. The atherogenic
lipoprotein phenotype is characterized by higher triacylglycerol and
decreased high density lipoprotein (HDL) cholesterol concentrations and
small low density lipoprotein (LDL) particles. A predominance of small
LDL particles is associated with a greater risk of CHD (Austin et al., 1990),
but it is not known if this association is independent of increased
triacylglycerol and decreased HDL cholesterol concentrations.
Table 11-2 and Figures 11-1 and 11-2 show that with decreasing fat and
increasing carbohydrate intake, plasma triacylglycerol concentrations